1. Field of the Invention
The present invention relates to a printer and a feeding control method.
2. Background Arts
As apparatuses for recording images on recording paper, there are ink-jet printer, thermal printer, and so forth. Each printer has a recording head with an array of plural recording elements, and records images by driving the recording head while feeding recording paper in a feeding direction.
When there is unevenness in feeding amount of recording paper (feeding unevenness), black and white streaks are likely to appear in recorded images. U.S. Pat. No. 5,988,790 discloses a recording method which carries out interlace recording by using the recording head with an array of N recording elements. The printer prevents streaks caused by feeding unevenness by alternately using first recording element and number N recording element for recording the same line. U.S. Pat. No. 6,328,400 discloses a recording method which feeds recording paper by a constant amount which is different from an interval between dot forming elements (such as recording nozzles) in the feeding direction (sub-scan direction). U.S. Pat. No. 6,328,400 discloses an art which makes streaks caused by feeding unevenness inconspicuous by setting an interval between dots smaller than the interval between dot forming elements.
However, gradation unevenness may appear periodically even if images are recorded by above recording methods. The periodical gradation unevenness is caused by unevenness in gear cutting in speed reduction mechanism which transfers the rotation of the feeding motor to the feeding roller. The black and white streaks may also periodically appear in recording paper by splicing the dots or by making the dots apart due to the feeding unevenness. It is difficult to quantitatively examine the amount of feeding unevenness caused by each factor, since the above factors affect the feeding unevenness in combination.
Japanese Patent Laid-Open Publication No. 7-52645 discloses a method for recording images, in which the recording paper feeding amount is changed by multiplying the pitch of recording elements by a random integer. Thereby, widths of recorded lines, which are recorded by the recording head, vary on a random basis. As a result, the streaks, which appear in the splice portion, become inconspicuous by changing the periodicity of streaks on a random basis. However, the black and white streaks, which appear in the splice portion of recording area due to periodical unevenness in the feeding amount, cannot be prevented effectively by applying the above feeding method, since the feeding amount is determined by the integral multiple of the pitch of the recording elements.